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Monsoonal Precipitation in a Model Hierarchy: Impact of Continental Geometry and Global Warming


Hui, Katrina Lynn (2022) Monsoonal Precipitation in a Model Hierarchy: Impact of Continental Geometry and Global Warming. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/k35s-mr12.


Monsoon systems around the world vary in their onset timing and precipitation spatial extent, suggesting that continental geometry could play an important role in differentiating between different monsoons systems. Since over half the world's population is dependent on monsoonal precipitation, it is of crucial importance to understand what controls the strength, seasonal evolution, and spatial extent of the tropical circulation and its associated precipitation and how they will evolve in a warmer climate. Recent studies suggest that individual monsoon regions will respond differently to climate change, highlighting the potential influence continental geometry may have on the current and future monsoon. In this thesis, we study the response of monsoonal precipitation, in its precipitation intensity, pattern, and onset timing, to idealized continent and climate change using a model hierarchy. By progressively building up complexity, we can gain insight from the idealized cases to determine responsible mechanisms in the responses to warming found in individual monsoon regions within the full general circulation models (GCMs).

First, we study the influence of continental geometry on the timing and spatial distribution of monsoonal precipitation under our current climate using an idealized aquaplanet model run with different zonally symmetric configurations of Northern Hemispheric land. We show that having continent extending to the tropical latitudes is necessary to generate monsoons that feature a rapid migration of the convergence zone over the continent, similar to observed monsoons. Without these regions, the tropical circulation is not able to rapidly transition into an angular momentum conserving monsoon regime. Next, we focus only on the effect of climate warming on the monsoon by using a set of idealized aquaplanet simulations with uniform mixed-layer depth, run with different atmospheric longwave optical depths to simulate a large range of both colder and warmer climates than the current climate. We show that as the climate warms, during the spring the atmospheric energy storage increases, which compensates the thermal forcing and allows for the tropical circulation transitions to be delayed, resulting in a delay in monsoon onset. Furthermore, we find that in extremely warm climates, the compensating effect of the energy storage is limited due to complex changes in the surface temperature seasonality. As a result, eventually the monsoon onset delay with warming saturates. These results highlight the important role the surface, both in its physical conditions and energy balance, has on setting the monsoon.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:monsoon; atmospheric circulation; atmospheric dynamics; climate; climate change; idealized simulation; tropical precipitation; tropical circulation;
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bordoni, Simona
Thesis Committee:
  • Schneider, Tapio (chair)
  • Bordoni, Simona
  • Thompson, Andrew F.
  • Su, Hui
Defense Date:14 March 2022
Non-Caltech Author Email:katonice (AT)
Funding AgencyGrant Number
Caltech Terrestrial Hazard Observation and Reporting CenterUNSPECIFIED
American Meteorological Society Graduate FellowshipUNSPECIFIED
Record Number:CaltechTHESIS:04192022-173428410
Persistent URL:
Related URLs:
URLURL TypeDescription DocumentArticle related to Ch. 2 DocumentArticle related to Ch. 3 DocumentArticle related to Ch. 2-3
Hui, Katrina Lynn0000-0003-0325-8800
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14554
Deposited By: Katrina Hui
Deposited On:20 Apr 2022 19:42
Last Modified:18 Nov 2022 21:15

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